General Science Mixed Quiz: Set 16

The correct answer is C, 240 J. Work done against gravity is weight multiplied by height, so 120 × 2 = 240 joules. Work is done when a force moves a body along the direction of that force, and it is measured as W = F × s. Here the boy must at least match the weight of the box, which is 120 N, and he moves it through 2 m, so the work done is 240 J. This work is stored in the box as gravitational potential energy, and the box would give back the same 240 J if it fell to where it started. Note that the weight is already given in newtons, so there is no need to multiply by g again. Option A is wrong because 60 J divides the weight by the height instead of multiplying. Option B is wrong because 120 J is only the weight in newtons, with the height left out. Option D is wrong because 130 J matches no step of the calculation. Exam tip: W = F × s, and work done against gravity is mgh, where mg is the weight.

The correct answer is C, Arthropoda. The name itself says so: in Greek arthros means jointed and podos means foot, so arthropods are the animals with jointed legs. They also have a hard outer skeleton of chitin, a segmented body and an open circulatory system, and they shed the skeleton as they grow, a process called moulting. Arthropoda is the largest phylum in the animal kingdom, holding insects, spiders, scorpions, crabs, prawns, centipedes and millipedes - about eighty out of every hundred known animal species. Option A is wrong because molluscs such as snails, octopus and mussels have a soft body with a muscular foot and usually a shell. Option B is wrong because nematodes are unsegmented roundworms like Ascaris, with no legs at all. Option D is wrong because echinoderms such as starfish and sea urchins are spiny-skinned marine animals that move on tube feet. Exam tip: Arthropoda - jointed legs, chitin skeleton, largest phylum; Mollusca is the second largest.

The correct answer is B, Archimedes' principle. It states that a body immersed wholly or partly in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced, so the apparent loss in weight of the body equals the weight of the displaced fluid. A body floats when the weight of fluid displaced equals its own weight, which is the law of flotation, and the same idea explains the ship, the submarine, the hydrometer and the lactometer.

Option A, Pascal's law, deals with the transmission of pressure through an enclosed fluid and explains hydraulic machines. Option C, Hooke's law, is about elasticity and states that within the elastic limit stress is proportional to strain. Option D, Boyle's law, is a gas law stating that at constant temperature the pressure of a fixed mass of gas is inversely proportional to its volume. The two fluid laws, Pascal and Archimedes, are the ones most often swapped in objective papers.

The correct answer is D, uterus. The zygote divides as it travels down the fallopian tube and the resulting ball of cells gets implanted in the thick lining of the uterus.

Fertilisation itself takes place in the fallopian tube, where a sperm fuses with the ovum to form the zygote. Repeated division turns it into an embryo, which reaches the uterus in about a week and sinks into the endometrium, the soft inner wall prepared by hormones. There the placenta develops and supplies the growing embryo with food and oxygen from the mother's blood while carrying away waste. Human pregnancy lasts about nine months.

Option A is wrong because the cervix is only the narrow neck of the uterus that opens into the vagina. Option B is wrong because the ovary produces the ovum and hormones but does not hold the embryo. Option C is wrong because the vagina is the passage that receives the sperm and later serves as the birth canal.

Exam tip: fertilisation in the fallopian tube, implantation in the uterus, nourishment through the placenta.

The correct answer is A, the conservation of energy. The first law says that the heat supplied to a system is equal to the increase in its internal energy plus the external work it does. Nothing is lost and nothing is created; energy only changes its form, which is the principle of conservation applied to heat.

Option B belongs to the second law, which introduces entropy and says that it never decreases in an isolated system. Option C belongs to the zeroth law, which says that two bodies each in thermal equilibrium with a third are in equilibrium with one another and which makes the measurement of temperature possible. Option D belongs to the third law, which says that the entropy of a perfect crystal tends to zero as the temperature tends to absolute zero and that absolute zero cannot be reached.

The correct answer is D, Lead and tin. Solder is an alloy of lead and tin, usually in nearly equal parts.

An alloy is a mixture of a metal with one or more other elements, made to gain a property the pure metal lacks. Solder is useful because the mixture melts at a far lower temperature than either lead or tin alone, so it flows easily and is used to join wires and electrical joints. Other alloys asked in papers are brass, made of copper and zinc, bronze of copper and tin, stainless steel of iron, chromium and nickel, and German silver of copper, zinc and nickel.

Option A is wrong because lead with copper is not the soldering alloy. Option B is wrong because tin with iron gives tin plating, used for tin cans. Option C is wrong because lead and iron together are not used as solder.

Exam tip: solder is lead plus tin and melts at a low temperature; brass is copper and zinc, bronze is copper and tin.

The correct answer is B, Iron rod. An iron rod is a solid, and the force of attraction between particles is strongest in the solid state.

In a solid the particles sit close together in fixed positions and can only vibrate, so a solid keeps its shape, has a definite volume and can hardly be compressed. In a liquid the attraction is weaker, so the particles slide over one another and the liquid takes the shape of its vessel while keeping its volume. In a gas the attraction is weakest and the particles move freely at high speed, so a gas fills any container and is easily compressed. The same order explains why solids have the highest density and gases the lowest.

Option A is wrong because water is a liquid with medium attraction. Option C is wrong because alcohol is also a liquid, and it evaporates faster than water. Option D is wrong because oxygen is a gas, where the attraction between particles is the weakest of all.

Exam tip: force of attraction is solid greater than liquid greater than gas, and the freedom of particles runs the other way.

The correct answer is D, Thallophyta. Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue. Most algae live in water, make their own food by photosynthesis and reproduce by spores; Spirogyra, Ulothrix, Chara and Volvox are common examples. Option A is wrong because angiosperms are flowering plants whose seeds lie enclosed in a fruit, the most advanced group of all. Option B is wrong because pteridophytes, such as ferns, are the first plants with proper vascular tissue, though they bear no seeds. Option C is wrong because bryophytes, such as mosses and Marchantia, are called the amphibians of the plant kingdom; they stand a step above thallophytes and need water for reproduction. Exam tip: the order of the plant kingdom is Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

The correct answer is C, Boron. Boron has three electrons in its outermost shell, so it is a trivalent element and is used as a p-type dopant. When a trivalent atom such as boron, aluminium, gallium or indium is added to silicon or germanium, it can form only three covalent bonds with its four neighbours, so one bond is left incomplete. That empty place is called a hole, it behaves like a positive charge carrier, and the doped crystal becomes a p-type semiconductor in which holes are the majority carriers. Adding a pentavalent atom instead leaves a free electron and gives an n-type semiconductor. Option A is wrong because arsenic has five valence electrons and is pentavalent. Option B is wrong because antimony is also pentavalent and is used for n-type doping. Option D is wrong because phosphorus has five valence electrons and donates an electron to the crystal. Exam tip: trivalent dopants such as boron, aluminium, gallium and indium give p-type material, while pentavalent ones such as phosphorus, arsenic and antimony give n-type.

The correct answer is C, Breaking a chalk stick. Force has to be applied to break the chalk because its particles hold one another together, and that pull is the force of attraction between particles.

Every substance is made of particles that attract one another, and the strength of that attraction decides how hard a thing is to break. The attraction is strongest in solids, less in liquids and least in gases, which is why an iron rod needs a hammer, water can be separated with a finger and air offers no resistance at all. The school activity of breaking chalk, then a pencil and then an iron nail shows the difference in this force from one solid to another.

Option A is wrong because compressing a sponge only squeezes out the air in its pores. Option B is wrong because dissolving sugar shows diffusion and the spaces between particles. Option D is wrong because heating ice shows a change of state, not the attraction itself.

Exam tip: attraction between particles is strongest in solids, weaker in liquids and weakest in gases.

The correct answer is B, kinetic energy. A stretched bow stores elastic potential energy, and when the string is released that store becomes the kinetic energy of the flying arrow. Potential energy is the energy held by a body because of its position or its shape. Pulling the string changes the shape of the bow, so the work done by the archer is stored as elastic potential energy, the same kind of store found in a compressed spring or a wound watch spring. On release the bow springs back to its old shape and pushes the arrow forward, so the stored energy turns into energy of motion. A small part does escape as the twang of sound and as heat, but the main change is potential to kinetic. Option A is wrong because chemical energy is stored in the bonds of fuels and food, not in a bent bow. Option C is wrong because the sound is only a small loss, not the main conversion. Option D is wrong because heat is likewise a minor loss here. Exam tip: a stretched bow, a compressed spring and a drawn catapult all store elastic potential energy.

The correct answer is A, 2. A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign. During one half cycle the upper diode conducts and during the next half cycle the lower diode conducts, and both send current through the load in the same direction, so the output has two pulses in every cycle. That is why a full wave rectifier gives a higher average output and a lower ripple than a half wave one. The other way to build a full wave rectifier is the bridge circuit, which uses four diodes but needs no centre tap. Option B is wrong because one diode makes a half wave rectifier that uses only half of each cycle. Option C is wrong because four diodes are used in a bridge rectifier. Option D is wrong because six diodes are used in a three-phase full wave rectifier. Exam tip: half wave 1 diode, centre-tap full wave 2, bridge 4.

The correct answer is C, one-sixth. Weight equals mass times the acceleration due to gravity, and the acceleration due to gravity on the moon is about one-sixth of its value on the earth because the moon has a much smaller mass and a smaller radius. A body of sixty kilograms therefore still has a mass of sixty kilograms on the moon but weighs only about a sixth of what it weighs on the earth, which is why astronauts can take long bounding steps there.

Options A and B, one-half and one-fourth, are invented fractions with no basis in the moon's mass and radius. Option D, the same, would be true of the mass of the body but never of its weight, and this is exactly the confusion the question is designed to catch. Remember the one-line rule: mass does not change with place, weight does, and on the moon the change is a factor of about one-sixth.

The correct answer is A, Archimedes' Principle. It states that the upthrust on a body dipped fully or partly in a fluid equals the weight of the fluid the body pushes aside. This is why a bucket of water feels lighter while it is still in the well, and why a ship of steel floats: its hollow shape displaces enough water to balance its own weight. The principle also gives the law of flotation and is used to find the purity of metals and the density of liquids with a hydrometer. B is wrong because Bernoulli's principle links the speed of a flowing fluid with its pressure, and explains lift on an aeroplane wing. C is wrong because the Beer–Lambert law deals with how much light a solution absorbs as it passes through. D is wrong because Pascal's law says pressure applied to an enclosed fluid is passed on equally in every direction, which is the basis of hydraulic brakes and lifts. Exam tip: Archimedes for buoyancy, Pascal for hydraulic press, Bernoulli for aerofoil lift.

The correct answer is A, the zeroth law. It states that if body A is in thermal equilibrium with body C, and body B is also in thermal equilibrium with body C, then A and B are in thermal equilibrium with each other. That is precisely what allows a thermometer to be used: the thermometer plays the part of the third body, and two objects that give it the same reading have the same temperature.

Option B, the first law, deals with energy accounting and not with the meaning of temperature. Option C, the second law, fixes the direction in which heat flows and sets a limit on the efficiency of engines. Option D, the third law, concerns behaviour near absolute zero. The zeroth law was recognised and named after the other three had already been numbered, which is why it carries the number zero.

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is B, Kinetic energy + Potential energy. The mechanical energy of a body is the sum of the energy of its motion and the energy of its position. Kinetic energy is half m v squared and gravitational potential energy is mgh, and their total stays the same as long as only gravity acts and friction is absent. That is the law of conservation of mechanical energy: a ball thrown upward loses kinetic energy and gains exactly as much potential energy, and a falling ball does the reverse, which is why a simple pendulum keeps swinging between the same two heights. When friction or air resistance acts, part of the mechanical energy turns into heat and sound, so it is no longer conserved, although the total energy of the system still is. Option A is wrong because chemical energy is stored in the bonds of fuels and food. Option C is wrong because heat is the energy of random molecular motion and is counted separately. Option D is wrong because electrical energy comes from moving charges. Exam tip: mechanical energy equals KE plus PE, and it stays constant only when no friction acts.

The correct answer is A, atmospheric pressure. A mercury barometer balances the pressure of the atmosphere against a column of mercury, which stands about 76 centimetres high at sea level. Mercury is chosen because it is very dense, does not wet glass and has a low vapour pressure; a water barometer would need a tube more than ten metres tall. A sudden fall in the barometer reading warns of a storm.

Option B, humidity, is measured by a hygrometer, the wet and dry bulb type being the common one. Option C, wind speed, is measured by an anemometer, usually with rotating cups. Option D, ocean depth, is found with an echo sounder or fathometer, which times a sound pulse reflected from the sea bed. Note also that the aneroid barometer, which uses no liquid, becomes an altimeter when its scale is marked in metres of height.

The correct answer is C, radiation. The space between the sun and the earth is very nearly empty, and radiation is the only mode of heat transfer that needs no material medium: energy travels as electromagnetic waves at the speed of light and is absorbed when it strikes matter.

Option A, conduction, requires particles in contact to pass energy along, so it cannot work across empty space. Option B, convection, requires a fluid that can itself move and carry energy with it, which again is not available between the sun and the earth, though convection does distribute that heat once it has entered the atmosphere. Option D fails for both reasons. A good absorber of radiation is also a good emitter, which is why a blackened surface warms fastest in the sun.

The correct answer is C, 24 J. By the work-energy theorem the work done equals the change in kinetic energy, which is half of 1.0 into 8 squared minus 4 squared, that is 0.5 × (64 - 16) = 24 joule.

Kinetic energy is given by half m v squared, so at 4 m/s the object has 8 joule and at 8 m/s it has 32 joule; the force must supply the difference of 24 joule. Note that doubling the speed makes the kinetic energy four times, because the speed is squared. The work-energy theorem holds whatever the path taken, which is why the question can be solved without knowing the force or the distance.

Option A is wrong because 8 joule is only the starting kinetic energy. Option B is wrong because 32 joule is the final kinetic energy, not the change. Option D is wrong because 16 joule comes from taking half of the difference of the squares of the speeds incorrectly.

Exam tip: work done = final kinetic energy minus initial kinetic energy, and doubling speed makes kinetic energy four times.